Valproic acid enhances etoposide induced cytotoxicity in neuroblastoma cells

Abstract

20010 Background: Metastastic neuroblastoma is resistant to treatment and prolonged response is difficult to achieve therefore new therapies are necessary. Etoposide, a topoisomerase II inhibitor is often used for its treatment. Valproic acid (VPA) has histone deacetylase inhibitor (HDI) activity. Epigenetic alterations described in neuroblastoma tumors make VPA a good candidate to evaluate for potentiation of etoposide-mediated cytotoxicity. We evaluate the effects of VPA in combination with etoposide in neuroblastoma cells. Methods: Human neuroblastoma cell lines SKNAS and SKNSH were incubated with 1.5 mM VPA and increasing concentrations of etoposide from 1x10-6 to 1 mM. Cell viability assay were measured with MTT assays. Results: We observed that VPA and etoposide independently decreased cell viability in a time and concentration dependent manner. The co-incubation with both drugs greatly enhanced the cytotoxicity of etoposide. IC50 for SKNSH cells treated with etoposide were approximately 1x10–3, 1.8x10–4, and 3x10- 5mM at 24, 72 and 96 hours, respectively. With the addition of VPA we found that cell viability was reduced approximately by 10 fold at each time point. At 72 and 96 hours 100 percent cell death was achieved at 0.1 mM of etoposide. IC50 for SKNAS cells treated with etoposide were approximately 1.8x10–3 mM and 6x10–4 mM at 72 and 96 hours, respectively. With the addition of VPA, IC50s were reduced by approximately 5 fold at the same exposure times. Further confirmation of synergistic activity was demonstrated with the use of the fraction product method of Webb formula. Conclusions: Our results demonstrate that VPA potentiates the cytotoxic effects of etoposide on neuroblastoma cells. by altering gene expression and rendering the cells more sensitive to etoposide induced cell death. Finally, since these agents have a proven track record of safety and efficacy in patients with neuroblastoma, this data supports the use of this combination in a phase I trial in patients with neuroblastoma. No significant financial relationships to disclose.